sedimentary
Chert Nodule
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale. Color: Off-white to light tan. Luster: Dull to waxy. Crystal Structure: Cryptocrystalline. Cleavage: None (Conchoidal fracture). Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Off-white to light tan
- Luster
- Dull to waxy
Identified More sedimentary →
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Physical properties
Hardness: 7 on Mohs scale. Color: Off-white to light tan. Luster: Dull to waxy. Crystal Structure: Cryptocrystalline. Cleavage: None (Conchoidal fracture). Specific Gravity: 2.65.
Formation & geological history
Formed in sedimentary environments, often through the replacement of limestone or chalk by silica-rich fluids. Often contains fossils and dates back to various geological periods from the Paleozoic to Cenozoic.
Uses & applications
Historically used for making stone tools (flint knapping). Modernly used as high-quality aggregate in construction, or for lapidary tumbling for hobbyists.
Geological facts
Chert nodules often contain perfectly preserved fossils of microscopic marine organisms. When struck together, they can create sparks, which led to their historical use in flintlock firearms.
Field identification & locations
Identified in the field by its extreme hardness (cannot be scratched by steel) and smooth, curved (conchoidal) fracture surfaces. Commonly found in limestone outcrops or as rounded pebbles in creek beds.
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